This invention relates generally to vertical axis wind turbines which employ vertically positioned airfoils as rotor blades. The centrifugal force acting on each blade in generally exceeds many times its weight, their ratio is often referred to as "g" loading. The efficiency of the vertical axis wind turbine depends on its tip speed to wind speed ratio here referred to as TR. For high efficiency this tip speed ratio TR ranges from 3 to 6 depending on the wind tubine geometry. The corresponding "g" loading acting at the center of gravity depends on the radial distance R and the wind speed V.sub..infin. and is given by ##EQU1## WHERE G.sub.C IS THE ACCELERATION OF GRAVITY.
For example, a wind turbine with TR = 3 at design wind speed V.sub..infin. = 20 km per hour will have a "g" loading of ##EQU2##
Thus even large radius rotors have a high "g" loading. To protect the structural integrety of the wind turbine it is essential that over speeding in high winds has to be prevented. Several techniques have been employed, such as
(A) INCREASING THE SHAFT LOAD AS A FUNCTION OF ROTOR RPM
(B) CONTROL THE ANGLE OF ATTACK OF THE ROTOR BLADE AIRFOIL AND THUS THE LIFT AND TORQUE PRODUCED
(C) ALLOW THE ROTOR BLADES TO FOLD OUTWARDS, THIS IS CALLED "CONING" AND ACTS MUCH LIKE A SAILBOAT WHICH LEANS OVER ON ITS SIDE IN A STRONG WIND SO AS TO REDUCE THE EFFECTIVE AREA OF ITS SAILS. This coning motion occurs in the direction of the centrifugal force, and because of the high "g" loading on the rotor blade it requires strong springs, levers or pulleys to balance the centrifugal force.